The broad range of this project covers several aspects in basic molecular virology and pathogenesis of enveloped viruses. The purpose is to identify and to understand the molecular mechanisms in viral entry, gene expression pathogenesis and assembly. The ultimate goal of these studies is the development of nonpathogenic viruses as highly specific gene delivery systems for the central nervous system. For the delivery of specific genes to the brain, possibly through the cerebral spinal fluid, enveloped viruses and particularly retroviruses are preferred viral candidates, however, nonenveloped viruses such as the nonpathogenic adeno-associated virus should also be evaluated. During the past FY, efforts by the Viral Replication Section toward these goals were limited. The main part of the study focused on the mechanism of pathogenesis by one enveloped virus, vesicular stomatitis virus (VSV). The possibility was explored to direct the pathogenic effect of VSV towards inhibiting another virus (HIV-1). We had earlier reported that the matric protein M of VSV alone is responsible for at least one cytopathic effect caused by the virus: the disruption of the cytoskeleton. The matrix protein was coexpressed with an infectious clone of HIV-1 in permissive HeLa T4 cells. This resulted in a dramatic inhibition of HIV-1 replication, The inhibition caused by the M protein was not specific for HIV-1, since the expression of other marker genes, all expressed by RNA polymerase II, was also inhibited, In fact, even the expression of a gene from a vaccinia virus recombinant was inhibited in the cytoplasm. The dramatic inhibition of HIV-1 by the M protein, did however, result in an effective protection of the entire cell population which was permissive for HIV-1. The potential use of the M gene for an intracellular immunization of cells against HIV-1 is currently under investigation. In addition, a chimeric glycoprotein between the VSV G protein and the HIV-1 Env protein was assembled by precise gene fusion. The goal was to change the ecotropic HIV-1 Env protein to an amphotropic glycoprotein, like the VSV G protein, by combining the receptor binding function of VSV G with the membrane fusion function of the HIV-1 Env protein. More extensive studies will be required, however, to be able to maintain the full dual function of such chimeric glycoproteins. A detailed knowledge of these structures will be essential for the specific targeting of cells in the central nervous system. Such systems could potentially be used for the therapy of neurological disorders and diseases such as Alzheimer's and Parkinson's diseases, multiple sclerosis, brain tumors, AIDS dementia, etc.